Turn string date from json to a Date object with Moshi

Question

with Gson you would do this

Gson gson = new GsonBuilder()
            .setDateFormat("yyyy-MM-dd'T'HH:mm")
            .create();

and pass it to the retrofit builder and Gson would make a Date object for you, Is there some way to get Moshi to do this too in a kotlin class?

Answer 1

If you’d like to use a standard ISO-8601/RFC 3339 date adapter (you probably do) then you can use the built-in adapter:

Moshi moshi = new Moshi.Builder()
    .add(Date.class, new Rfc3339DateJsonAdapter().nullSafe())
    .build();

JsonAdapter<Date> dateAdapter = moshi.adapter(Date.class);
assertThat(dateAdapter.fromJson("\"1985-04-12T23:20:50.52Z\""))
    .isEqualTo(newDate(1985, 4, 12, 23, 20, 50, 520, 0));

You’ll need this Maven dependency to make that work:

<dependency>
  <groupId>com.squareup.moshi</groupId>
  <artifactId>moshi-adapters</artifactId>
  <version>1.5.0</version>
</dependency>

If you want to use a custom format (you probably don’t), there’s more code. Write a method that accepts a date and formats it to a string, and another method that accepts a string and parses it as a date.

Object customDateAdapter = new Object() {
  final DateFormat dateFormat;
  {
    dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm");
    dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
  }

  @ToJson synchronized String dateToJson(Date d) {
    return dateFormat.format(d);
  }

  @FromJson synchronized Date dateToJson(String s) throws ParseException {
    return dateFormat.parse(s);
  }
};

Moshi moshi = new Moshi.Builder()
    .add(customDateAdapter)
    .build();

JsonAdapter<Date> dateAdapter = moshi.adapter(Date.class);
assertThat(dateAdapter.fromJson("\"1985-04-12T23:20\""))
    .isEqualTo(newDate(1985, 4, 12, 23, 20, 0, 0, 0));

You need to remember to use synchronized because SimpleDateFormat is not thread-safe. Also you need to configure a time zone for the SimpleDateFormat.